The requirements on the capacity of the transmission network nodes have been growing along with the rapid growth of network traffics. However, single-subrack transmission equipments are subject to size and power consumption limits and thus can offer only limited growth in the equipments' cross-connect capacity, which cannot catch up with the speed of network traffic growth.
In order to provide larger cross-connect capacity, multiple subrack cascade can be used to build a cluster cross-connect system, i.e., connect at least two cable subrack and cross-connect subrack via optical fiber to build a cross-connect system with super large capacity. In the equipments in such cluster cross-connect system, 3-stage CLOS matrix is usually used as multilevel cross-connect matrix.
In a technical scheme of the prior art, electrical cross-connect subrack is used to realize cluster cross-connect system. In a cluster cross-connect system using electrical cross-connect subracks, the second stage uses electrical cross-connecting. Since the second stage uses electrical cross-connecting and supports cross-connect matrix of cross-connecting at smaller granularity, the signal rate of interconnection signals between subracks is higher and the number of interconnecting optical fibers can thus be reduced.
But the power consumption and the size of the cluster cross-connect system using electrical cross-connect subracks are large. In addition, as synchronization is difficult by using electrical cross-connect subrack, the 3-stage cross-connect matrix may need to be designed to support strict sense non-blocking, i.e., the output capacity of the first stage cross-connect basically needs to be 1 times more than the input capacity (and the number of basic cross-connect units in the second stage will need to double accordingly, the situation of the third stage is similar to the first stage), which will lead to much growth in the number of interconnecting optical fibers between subracks and the power consumption and the size of cross-connect subracks.
In an alternative technical scheme of the prior art, Micro-electromechanical System (MEMS) is used directly to switch the cross-connect granules, i.e., the basic cross-connect units in the second stage of the cluster cross-connect system consist of MEMS devices which switch signals directly in the optical layer. Since there is no need to cross connect in the electrical layer in the second stage, the power consumption of the cross-connect subracks can be reduced significantly.
However, the overall interconnection rate of the cluster cross-connect system using MEMS is too low and too many interconnecting optical fibers are needed. In addition, the switch speed of the MEME devices is very slow, hence the cluster cross-connect system using MEMS can only adopt strict sense non-blocking, too, which further increases the number of interconnecting optical fibers and cross-connect subracks.